An agricultural harvester known as a “combine” is historically termed such because it combines multiple harvesting functions with a single harvesting unit, such as picking, threshing, separating and cleaning. A combine includes a header which removes the crop from a field, and a feeder housing which transports the crop matter into a threshing rotor. The threshing rotor rotates within a perforated housing, which may be in the form of adjustable concaves, and performs a threshing operation on the crop to remove the grain. Once the grain is threshed it falls through perforations in the concaves and is transported to a grain pan. From the grain pan the grain is cleaned using a cleaning system, and is then transported to a grain tank onboard the combine. The cleaning system includes a cleaning fan which blows air through oscillating sieves to discharge chaff and other debris toward the rear of the combine. Non-grain crop material such as straw from the threshing section proceeds through a straw chopper and out the rear of the combine. When the grain tank becomes full, the combine is positioned adjacent a vehicle into which the grain is to be unloaded, such as a semi-trailer, gravity box, straight truck, or the like; and an unloading system on the combine is actuated to transfer the grain into the vehicle.
In combines with headers that are rigidly attached to the combine feeder house, the combine is typically equipped with a header height control (HHC) system which adjusts the height and tilt angle of the header relative to the ground. The HHC system is particularly important to prevent the header from contacting objects in the field as the combine harvests crop material and also helps to keep the cutting apparatus of the header at a desired height relative to the ground in order to obtain the desired crop collection. Known HHC systems include an actuator linked to a frame of the header, sensors which detect the height of the cutting apparatus relative to the ground, and a controller which controls the actuator based on the sensed height of the cutting apparatus. One type of sensor that can be utilized is a cutter sensor which contacts the ground and, based on the flexing of the sensor, determines the relative height of the cutting apparatus to the ground. A known problem with such cutter sensors is that once the cutter sensor is off the ground, the HHC system cannot accurately determine whether the cutter sensor is two inches or two feet above the ground and therefore cannot reliably determine how to adjust the height and/or tilt angle of the header to return the header to the desired position.
Some headers also include one or more spring loaded gauge wheels which stay in contact with the ground and help keep the header level as the combine travels across the field. One particular problem that is encountered with such gauge wheels occurs when the header travels over a large terrain irregularity which causes the cutter sensor to leave the ground and the spring of the gauge wheel(s) to fully compress. In such a situation, the biasing force from the spring into the ground attempts to lift the header and, due to the rigid connection of the header to the combine, the combine off the ground. This is further compounded by the HHC system sensing that the cutter sensor is off the ground and attempting to lower or tilt the header toward the ground in order to return the cutter sensor, and thus the cutting apparatus, back to the ground. The net effect of these simultaneous motions can cause the front of the header to be pointed into the ground as the combine moves forward, forcing the header to dig into the ground and potentially causing significant damage to the header and the combine.
What is needed in the art is a HHC system that can overcome some of the previously described disadvantages of known HHC systems.